Adds CachedBatch, EntityCacheEntry, and EntityClassificationCache with
just TryGet (returns false on empty). The skeleton compiles and the first
test (TryGet_EmptyCache_ReturnsFalse) passes. Subsequent tasks add
Populate, InvalidateEntity, InvalidateLandblock, and the dispatcher
integration. Per spec design Section 6.1.
Note: CachedBatch / EntityCacheEntry / EntityClassificationCache are
internal (not public as the plan snippet showed). Their members
transitively reference the internal GroupKey type, so promoting them to
public produces CS0051 inconsistent-accessibility errors. The cache is
dispatcher-internal coordination state anyway, and the AcDream.App
csproj already exposes internals to AcDream.Core.Tests via
InternalsVisibleTo, so the test sees everything it needs.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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